Internal combustion engines include intake and exhaust valves that can be actuated by cam lobes of at least one camshaft. In some configurations the camshafts are constructed with sliding camshaft assemblies having multiple steps for varying the lift distance of an engine valve. For example, a two-step sliding camshaft may include a high lift cam lobe position for lifting an engine valve to a maximum distance, and a low lift cam lobe position for lifting the engine valve below the maximum lift distance.
At least one sliding camshaft actuator is fixed on an internal combustion engine for changing position between the multiple cam lobes. Particularly, at least one actuator pin of a camshaft actuator is operative to selectively engage displacement grooves configured on the periphery of camshaft barrels formed on the sliding camshaft assembly. As the camshaft assembly rotates, an actuator pin is selected to move into a displacement groove of the camshaft barrel which causes the sliding camshaft assembly to shift into a different position along the camshaft axis. When a sliding camshaft shifts position, the intake and/or exhaust valves are actuated differently in accordance with the changed cam lobe position, e.g., a sliding camshaft may move from a high lift cam lobe position to a low lift cam lobe position, which in turn will cause the engine operation to be different.
Thus, the sliding camshaft actuator is an important component in the proper operation of a VVL sliding camshaft system, particularly the actuator's pin position relative to extending into, and retracting from, the displacement grooves formed in the camshaft barrels. The actuator's pin position is tracked by a sensing device which outputs a digital signal indicative of the pin position, e.g., a duty cycle value that represents the amount of distance the pin is ejected from the solenoid; a high value of duty cycle equals retracted while a low value of duty cycle equals ejected (max distance). Monitoring the pin position sensor output signal allows the engine controller to determine if the camshaft actuator is responding properly to its commands to actuate the pin(s) to change variable valve lift status as well as determine if the pins are being acted upon appropriately by the physical ramp geometries present in the grooves that guide the sliding cam barrels.
In addition to having a means for monitoring a camshaft actuator's pin position in response to a command, there is a need for a means to determine if the actual pin position is correct in accordance with the command provided to ensure intended engine performance is a achieved.